signaled the PC to go back on-hook, the DTR is dropped. For this to happen, the modem must
be configured to interpret the loss of the DTR as the end of a conversation. When the DTE drops
the DTR, the modem is alerted that the carrier is no longer needed.
each call, or it can be scripted in a chat script that is sent to the modem each time a call is
terminated. Each time a call is terminated, the router resets (rescripts) the modem. This low
level configuration is done on the modem to prepare the modem for reuse. In many cases,
accepting the default configuration for a modem allows it to function properly.
of each modem parameter are discussed in the section, "Configuration of an Attached Modem,"
later in this chapter.
end modem must signal the near-end DTE that the transmission has been terminated. The
modem must be programmed to understand and signal this termination. In other words, the
modem must be told how to handle the loss of carrier detection. By default, most modems
understand that this signal loss is an indication that the call is to be terminated. However, it is a
configuration parameter that the modem must understand.
reverse Telnet connection. A host that is connected to a router can Telnet to a Cisco reserved
port address on the router and establish an 8-N-1 connection to a specific asynchronous port.
An 8-N-1 connection declares the physical signaling characteristics for a line.
and an asynchronous port. To establish a connection to the modem connected to the
asynchronous port, you can Telnet to any valid IP address on the router and declare the Cisco
reserved port number for the asynchronous interface. You can do this only, however, from the
router console or a remote device that has Telnet access to the router.
addition, the use of reverse Telnet enables the administrator to configure locally attached
devices. For example, suppose you want to set up an 8-N-1 connection to the first asynchronous
interface on a router, which has the 123.123.123.123 address assigned to its E0 port. To connect
in character mode using Telnet, you would issue the following command: